Switch libwebsockets license link to Github (#1727)

The libwebsockets website is down, so our [end-to-end tests are
currently
broken](https://app.circleci.com/pipelines/github/tiny-pilot/tinypilot-pro/3814/workflows/dd6cf195-4597-48ff-a1a3-f796b80dcbc6/jobs/35466)
due to that.

This happened one or two times in the past already, and [this comment
from the libwebsocket
maintainer](warmcat/libwebsockets#3053)
suggests that it might be more reliable for us to use Github for
referencing the sources.

We can otherwise also wait a bit to see whether things may eventually
settle.
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---------

Co-authored-by: Jan Heuermann <jan@jotaen.net>

app/license_notice.py

@@ -202,8 +202,13 @@ class LicenseMetadata:
     LicenseMetadata(
         name='libwebsockets',
         homepage_url='https://libwebsockets.org',
+        # In the past, we used to link to the license that was hosted on the
+        # git mirror at libwebsockets.org/git. We repeatedly experienced
+        # outages of their website, however, so for reliability reasons, we now
+        # link to Github instead.
+        # (See https://github.com/tiny-pilot/tinypilot/pull/1727)
         license_url=
-        'https://libwebsockets.org/git/libwebsockets/tree/LICENSE?h=v3.2-stable',
+        'https://github.com/warmcat/libwebsockets/blob/v3.2.2/LICENSE',
     ),
 
     # Fonts.